There are many situations in which it is desirable or necessary to apply a mechanical, releasable balanced compressive load to an assembly. For example, in certain types of separable electrical connectors, a compliant interposer connector (a sheet of anisotropic conductive elastomer (ACE) material) is compressed between an electrical device and a corresponding array of electrically conductive pads on a substrate (e.g. a printed circuit board). The interposer conducts electricity vertically between each pad on the device and the corresponding pad on the substrate, while electrically isolating the pads from their laterally-adjacent neighbors. This has been done using a spring preload to compress the ACE between the device and the substrate.
One method of spring preloading such a system has been to have a flat, rigid backup plate below the substrate with four pins or bolts going up through four corresponding holes in the substrate. The interposer connector sits on pads on the top surface of the substrate; the device sits on the interposer connector; and a rigid plate, typically a heat sink, sits on the device. The four pins passing through the substrate typically go through clearance holes in the interposer connector, and extend upwards past the device through holes or slots in the heat sink. Above the heat sink, lock washers and nuts are placed on the ends of the pins. Tightening these nuts pulls the heat sink down, compressing the substrate/interposer connector/device stack-up between the backup plate and the heat sink. The advantage of this system is that the device can be replaced without accessing any hardware below the substrate. The disadvantage of this system is that the forces on the four pins must be carefully balanced to compress the system evenly.
Another disadvantage of this system is that the compressive spring element is the interposer itself, but the interposer in general has poor spring characteristics. In one modification of the above-described system, coil springs are placed over each of the four posts, between the heat sink and the washer/nut assembly. The springs can be designed to assure a quality compressive load. The problem of carefully tightening the springs to assure a balanced load remains a disadvantage of this design.
Another method of spring preloading the system has been to have four pins or bolts dropping down from the heat sink, through clearance holes in the interposer connector, the substrate, and a flat rigid backup plate. Holes or slots in a spring plate located below the rigid backup plate engage the four pins. The center of the spring plate has a threaded insert. The system is compressed using a set screw passing through the spring plate and engaged in the threaded insert by forcing the set screw against the backup plate, thus flexing the spring plate and compressing the substrate/interposer connector/device stack-up between the backup plate and the heat sink. The advantage of this system is that the forces on the stack-up are intrinsically centered since the only load applied to the backup plate is applied at its center. The disadvantage of this system is that the device cannot be replaced without accessing both the device side of the substrate and the set screw in the spring plate on the opposite side of the substrate. In many instances, access to the bottom of the board is not available.
Orthogonal interconnection electrical connectors, such as used with circuit pack to backplane interconnection, have several unique characteristics that must be addressed when developing a high performance connector system. For one, the connector must be capable of being physically actuated (connected and/or released) from the opposite end of the circuit pack (daughter board) from the connector. This separation can be as much as 24″. Another limitation is that the mating of the circuit pack to the backplane is a blind mate that requires an alignment system specific to the structure. Also, backplanes are often bowed out of plane by the assembly process and the force of inserting the circuit pack. The forces causing the bowing must be counteracted. Still further, uniform loading and controlled positioning of the circuit pack relative to the backplane is required to achieve high performance.
In some such orthogonal connectors, sequencing of the order of make/break of individual contacts such as power and ground may be required. The ability to mix different types of contacts, such as power and fiber optic contacts, may also be required.
The above-described issues become more complex for high performance connectors, in which tight tolerance control is required to achieve the performance.